In the past, suspension systems in general have been used for many applications, including cushioning impacts, vibrations or other disturbances experienced by vehicles and machinery. Typical applications, for example, include the use of suspension systems in bicycles, motorcycles and all-terrain vehicles ("ATVs").
For example, bicycles have been developed with suspension systems for cushioning impacts or vibrations experienced by a rider when the bicycle contacts bumps, ruts, rocks, pot holes or other obstacles and road variations. Typically, such bicycle suspension systems have been configured for use in the front or rear bicycle fork, in the head tube that connects the front fork to the bicycle frame and handlebars, in the seat post, and in conjunction with a rear wheel swing-arm assembly, among other locations.
For example, locating bicycle suspension systems within bicycle forks has become increasingly popular. Bicycle suspension forks typically comprise at least one fork leg, and usually comprise two such legs, each leg including first and second telescoping tubular elements (an inner tubular element slidable within an outer tubular element). Typically, the inner tube is the upper tube and the outer tube is the lower tube, although the reverse may also be true. A resilient expansion biasing element, such as a spring, biases the tubular elements apart, but permits the inner tube to slide into the outer tube as necessary.
Bicycle fork suspension systems have often included expansion biasing elements such as coil springs, elastomer springs, arcuate spring discs, leaf springs, gas springs such as air springs, among other types of springs used for nominally biasing the tubular elements apart from one another and for absorbing compression forces applied to the forks as a result of impacts and vibrations experienced during operation of the bicycle. Using biasing elements in this way permits the tubular elements to compress in response to an impact or other force input, and expand or rebound once the force is removed, so that the first and second tubular elements return to their original spaced-apart positions relative to each other. Such bicycle suspension systems have also included expansion biasing elements in combination with damping devices such as hydraulic damping or friction damping mechanisms, which absorb some of the energy imparted to the bicycle by impacts or other force inputs causing compression or rebound of the tubular elements, thereby resisting movement of the tubular elements relative to each other.
One problem associated with prior suspension systems, and particularly with vehicle suspension systems such as those incorporated into bicycle suspension forks, is that they have been unnecessarily heavy. For example, the weight of a bicycle fork affects the handling of the bicycle, and adds to the overall weight of the bicycle, which the rider must work to propel and control. Reducing weight is therefore of great concern to all bicycle riders, and particularly to those involved in racing applications, where a reduction in weight offers an important competitive advantage. Accordingly, there is a need for suspension systems, and particularly for bicycle suspension systems, that are designed to be light-weight.
In the past, weight savings have been achieved in suspension systems such as bicycle suspension forks by using a gas spring as the expansive biasing element, instead of heavier biasing elements such as metal coil springs and the like. The resulting gas-sprung designs have suffered from disadvantages, however, including limited tunability of the suspension system's spring rate ("spring rate" may be defined as the amount of force required to compress or expand the suspension system a given distance) and, therefore, an inability to accommodate a wide variety of rider preferences. Consequently, there is a need for gas-sprung suspension systems, and particularly for gas-sprung bicycle suspension systems, that are designed to be fully tunable.
One adjustment feature that has been incorporated into gas-sprung suspension systems such as bicycle suspension forks is the ability to increase or decrease the gas pressure in the suspension system. In bicycle suspension forks as in other suspension systems, one problem associated with this adjustment feature is that an increase or decrease in the fork gas pressure results in a corresponding increase or decrease in the compressive force required to be applied to the fork before the first and second tubular elements will begin to compress in response to a bump or other force input (this force is commonly known as the "crack force"). Thus, depending upon the gas pressure in the gas spring, the suspension system may be undesirably stiff, and adequately responsive only to large inputs.
In gas-sprung bicycle suspension forks, for example, if the crack force is too large for a given rider, the fork will act much like a rigid, unsuspended fork in response to relatively small force inputs. If the crack force is too small, the fork tubes will compress easily and may sag extensively in response to the rider's weight, thus reducing their available compressive travel during use. Neither condition is desirable, and the wide range of potential rider weights and preferences makes the use of a pre-set or inadequately adjustable crack force problematic. Thus, there is a need for gas-sprung suspension systems, and particularly for gas-sprung suspension bicycle systems, that are designed to have an improved adjustment feature for adjusting the crack force of the system.
Particularly for bicycles, with respect to which weight is a constant concern, the ability to achieve multiple performance goals using a single system is highly attractive. Specifically, bicycle suspension systems require a "top-out" bumper for preventing impacts of the two tubular elements upon overexpansion, which typically occurs when the suspension system rebounds after a compression, or when the wheel of the suspended vehicle is lifted off the ground. Such impacts, which are particularly frequent for suspension systems used on mountain bikes, cause undesirable noise and may cause structural damage over time. In the past, various types of springs have been used to cushion top-out impacts. Gas springs, however, have not been used or recognized as being usable as top-out bumpers. As recognized by the present invention, however, the progressive spring rates and other features of gas springs give them a unique potential of providing a gradual, readily tunable resistance to top-out impacts. Accordingly, there is a need for gas-sprung suspension systems, and particularly for gas-sprung suspension bicycle systems, that integrate crack force and spring rate adjustment features with the ability to resist top-out impacts.
Typical suspension systems also frequently require a damping system. A typical damping system for use in a bicycle fork suspension system, for example, utilizes a valved piston and a damping fluid (or gas) which selectively passes through ports or apertures in the piston valves. Flow of the damping fluid through the piston valves, and thus damping, is controlled by the size of piston ports of the piston valve. The adjustability of damping characteristics, as well as reducing the weight of the damping system, have been ongoing concerns for suspension systems generally, and for bicycle suspension systems in particular. Accordingly, there is an ongoing need for suspension systems, and particularly for bicycle suspension systems, that are lightweight, yet which provide the above-described features, such as appropriate biasing, spring rate and crack force adjustability, and damping.
Accordingly, one object of the present invention is to provide a suspension system, and particularly a bicycle suspension system, that is lightweight.
Another object of the present invention is to provide a gas-sprung suspension system, particularly for gas-sprung bicycle suspension systems, that are fully tunable.
A further object of the present invention is to provide a gas-sprung suspension system, and particularly a gas-sprung bicycle suspension system, that has an improved adjustment feature for adjusting the crack force of the system.
Yet another object of the present invention is to provide a gas-sprung suspension system, and particularly a gas-sprung bicycle suspension system, that integrates crack force and spring rate adjustment features with a feature for resisting top-out impacts.
Yet another object of the present invention is to provide a bicycle suspension system, that is lightweight and provides appropriate biasing, spring rate and crack force adjustability, and damping.